1. Field of the Invention
The present invention relates to a wavelength converter applicable to a network based on wavelength-division multiplexing (WDM) transmission in optical communication systems.
2. Related Background Art
Because of the developments of the WDM transmission technologies and optical amplifiers, WDM networks have been studied extensively by many researchers. Interconnection of the WDM systems that are independently designed and constructed is required cost effectively. For the purpose of satisfying the requirements, several types of the wavelength conversion techniques have been studied. Fiber-optic four-wave mixing (FWM) based parametric wavelength conversion is one of the very promised techniques for applying to the broadband WDM networks because of its bit-rate transparency (response timexcx9c100 fs), and its ability to process the multi-channels optical signals simultaneously. It is known that the FWM based parametric wavelength conversion is also realized in semiconductor optical amplifiers (SOA""s). Since the multi-channels simultaneous wavelength conversion is realized by optical parametric processes in nonlinear media, it seems that so far most of the researchers have devoted to broaden the bandwidth of the wavelength conversion in wavelength domain to follow the increment of the extraordinary number of channels. However, from the practical point of view, not only the broadband multi-channels simultaneous wavelength conversion, but also different applications of the parametric wavelength conversion to the WDM networks should be conceived to enhance the flexibility of the signal processing.
An object of the present invention is to provide a wavelength converter in which only some lightwaves that are the constituent of all the WDM lightwaves, are filtered out in frequency domain, then only the filtered out lightwaves are wavelength converted parametrically by use of FWM in optical fiber or in SOA, and to provide WDM transmission methods in which the above types of the parametric wavelength converter is applied to enhance the flexibility of the wavelength routing and signal processing in WDM networks.
Because of its frequency dependence of the transmittance and/or reflectivity of the filtering components, such as dielectric thin films and gratings, some lightwaves that are constituent of the inputted WDM lightwaves (hereafter referred as the original WDM lightwaves), can be filtered out then transmitted (or reflected) lightwaves are outputted from the one output port. The remained lightwaves not to be transmitted (or not to be reflected) are reflected (or transmitted) and outputted from the other output port. Solely the transmitted (or reflected) lightwaves outputted from the components can be simultaneously wavelength converted by the parametric wavelength converter concatenated with after the filtering components. The present invention provides a wavelength converter in which the lightwaves, that are required to be wavelength converted, are filtered out by one or more filtering components, then the filtered out lightwaves are simultaneously wavelength converted by a FWM based parametric wavelength converter. The present invention provides further a wavelength converter in which, WDM lightwaves are divided by an optical divider, the one divided WDM lightwaves are outputted from the one output port of the divider directly. The other lightwaves are outputted from each the remained output port and lightwaves outputted from each output port are wavelength converted independently. The wavelength converted WDM lightwaves after outputted from the output ports, and the WDM lightwaves not to be wavelength converted after outputted from the divider, are combined with together without duplicating in frequency domain. The present invention also provides wavelength-division multiplexing transmission methods using the FWM based parametric wavelength converters concatenated with after the optical filters or the optical dividers.
According to a first aspect of the present invention, there is provided a first wavelength converter by use of four-wave mixing (FWM) in an optical fiber or a semiconductor optical amplifier (SOA), in which one or more channels of the lightwaves are filtered out from the original wavelength-division multiplexed (WDM) lightwaves using optical filters, and the channels of the filtered out WDM lightwaves are launched into the wavelength converter as the lightwaves required to be wavelength converted, and solely the lightwaves required to be wavelength converted are wavelength converted.
According to a second aspect of the present invention, there is provided a second wavelength converter in which, in the first wavelength converter, the lightwaves required to be wavelength converted are obtained from the original WDM lightwaves by applying optical filters, and the wavelength converted lightwaves are obtained from the filtered out lightwaves by use of the FWM in an optical fiber or in an SOA, and the wavelength converted lightwaves are combined with one or more lightwaves not to be filtered out by the optical filter in order to provide an alternative channel configuration of the WDM lightwaves to the original WDM lightwaves in wavelength domain.
According to a third aspect of the present invention, there is provided a third wavelength converter in which, in the first wavelength converter, the wavelength converted lightwaves are combined with one or more extra lightwaves any of whose wavelength is not coincided with all the wavelength of the wavelength converted lightwaves to provide an alternative channel configuration of the WDM lightwaves to the original WDM lightwaves in wavelength domain.
According to a fourth aspect of the present invention, there is provided a fourth wavelength converter in which, in any one of the first to third wavelength converter, one or more filter type optical components are used to filter out the lightwaves periodically at N channels (N is an integer) spacing from the original WDM lightwaves by each components, then the lightwaves that are filtered out by each filter type optical component are wavelength converted independently or simultaneously by use of the FWM in an optical fiber or in an SOA.
According to a fifth aspect of the present invention, there is provided a fifth wavelength converter in which, in the fourth wavelength converter, N filter type optical components capable to filter out the lightwaves periodically at N channels (N is an integer) spacing from the original WDM lightwaves are used, then the one or more of the filtered out lightwaves are wavelength converted independently or simultaneously by use of the FWM in an optical fiber or in an SOA, and the wavelength converted lightwaves are combined with the lightwaves not to be filtered out to provide an alternative channel configuration of the WDM lightwaves whose channel interval is larger than that of the original WDM lightwaves inputted to the wavelength converter.
According to a sixth aspect of the present invention, there is provided a sixth wavelength converter in which, in any one of the first to third wavelength converter, total wavelength bandwidth of the original WDM lightwaves inputted to the wavelength converter are virtually divided into n (n is an integer) local wavelength bands (hereafter referred as xe2x80x9csub-bandsxe2x80x9d and not necessary all the bandwidth of the sub-bands are equivalent), and filter type optical components are used to filter out one or more sub-bands from the original WDM lightwaves, and the sub-bands that are filtered out by the optical components are wavelength converted independently or simultaneously by use of the FWM in an optical fiber or in an SOA.
According to a seventh aspect of the present invention, there is provided a seventh wavelength converter in which, in the sixth wavelength converter, nxe2x88x921 filter type optical components capable to filter out the lightwaves of the j-th sub-band (j is an integer) from the original WDM lightwaves are used, and the lightwaves inside one or more of the sub-bands are filtered out by each filter, and the filtered out sub-bands are wavelength converted independently or simultaneously, and the wavelength converted lightwaves are combined with the lightwaves not to be filtered out to provide an alternative channel configuration of the WDM lightwaves whose channel interval in frequency domain is smaller than that of the original WDM lightwaves.
According to an eighth aspect of the present invention, there is provided an eighth wavelength converter in which, output port of the fourth or fifth wavelength converters is connected with input port of a wavelength demultiplexing devices to demultiplex the wavelength converted WDM lightwaves whose frequency interval is expanded by the fourth or fifth wavelength converter in comparison with the original WDM lightwaves, thereby providing a wavelength demultiplexing module.
According to a ninth aspect of the present invention, there is provided a ninth wavelength converter in which using four-wave mixing (FWM) in an optical fiber or a semiconductor optical amplifier (SOA), in which one or more wavelength-division multiplexing (WDM) lightwaves are divided by an optical divider, and lightwaves output from the one or more output ports of the divider are wavelength converted by use of the FWM in an optical fiber or in an SOA.
According to a tenth aspect of the present invention, there is provided a tenth wavelength converter in which, in the ninth wavelength converter, the lightwaves outputted from the one output ports of the divider are combined with the wavelength converted lightwaves that are converted after outputted from the other output ports of the optical divider, without any duplication in frequency domain to increase numbers of the WDM lightwaves.
According to an eleventh aspect of the present invention, there is provided an eleventh wavelength converter in which, in the ninth wavelength converter, the wavelength converted lightwaves after outputted from the optical divider are combined with one or more lightwaves any of whose wavelength is not coincided with all the wavelength of the wavelength converted lightwaves to provide an alternative channel configuration of the WDM lightwaves to the original WDM lightwaves in wavelength domain.
According to the twelfth aspect of the present invention, there is provided a first wavelength-division multiplexing (WDM) transmission method in which wavelength converted WDM lightwaves whose frequency intervals are made wider than the wavelength intervals of the original WDM lightwaves by use of the fourth or fifth wavelength converter, are transferred from an optical communication system whose transmission line is composed of the optical fiber less influenced by the inter-channel crosstalk to a system whose transmission line more influenced by the crosstalk than the other transmission line.
According to the thirteenth aspect of the present invention, there is provided a second WDM transmission method in which WDM lightwaves whose frequency intervals are made narrower than the frequency intervals of the WDM lightwaves by use of the sixth or the seventh wavelength converter, are transferred from an optical communication system whose transmission line is composed of the optical fiber easily influenced by the inter-channel crosstalk to a system whose transmission line is less influenced by the crosstalk than the other transmission line.
According to the fourteenth aspect of the present invention, there is provided a third WDM transmission method in which, in the second WDM method, additional external WDM lightwaves are combined with the wavelength converted lightwaves to increase channel numbers, and the frequency interval of the combined lightwaves are narrower than the interval of the original WDM lightwaves by use of the sixth or the seventh wavelength converter, and the resultant WDM lightwaves are transmitted.